Pocket 6k Pro issues getting video feed for multiple cameras

Hi all,
I am wondering if anyone has found a good solution to getting multiple 6k pro's onto a single monitor for video village. We currently have 8 cameras, and recently started using 5 plus on a single setup. I can use teradeks/ blackmagic hmdi to sdi converters to get a couple into a flanders, but ideally would like to use something like this:
"PORTTA Quad Multi Viewer Seamless Switcher 4 in 2 Out" from Amazon to get 4 onto a single tv/ monitor. Unfortunately with the unit above I can't get an image from the cameras to display (unit works, tv works, direct from camera to tv works.)

Does anyone have a working solution out there to skip SDI and get multiview from several cameras direct via hdmi? Thanks for your time and expertise!

An ATEM Extreme would give you the 8 sources in a Multiview.

Thanks Jim,
We have the ATEM mini, but unfortunately we need to record external audio, and have no way to time code sync when using the ATEM. So the best solution is just get multiview outside the ATEM system, however I can't seem to find a device that will work with the BMPCC's. I have purchased 2 hdmi multivew/ matrix boxes and neither have been able to produce display from the cameras.

So just after my last post, my co-worker was able to get the second 4k multi viewer to work! We had noticed through other forum posts that HDMI accessories from the brand "J-Tech" had worked for other people, so I bought their multi viewer to try, and it does work with the BMPCC6K. I can't posts links, but it is called: 4x1 HDMI Multi-viewer & Seamless Switcher 4K 60Hz | 4 in 1 Out. And can be purchased from the jungle river based website.